DLC for Capcom's Resident Evil 6 will be released first on Xbox 360 via a timed exclusivity agreement.
The deal wasn't actually mentioned in Capcom's impressive E3 demo, though confirmation was flashed on the screen at the end.
Microsoft had just moments before confirmed DLC exclusivity for Square Enix's Tomb Raider, though it's not yet clear if that's timed or total exclusivity.
As for Resident Evil 6, Microsoft treated the audience to an action-packed sequence from the game featuring Leon Kennedy fleeing from an attacking helicopter. Then escaping in a helicopter. Then crashing in a helicopter.